1. Field of the Invention
The present invention relates to a developing device, a process cartridge, and an image forming apparatus to be used in an image formation operation of an electrophotographic printing method.
2. Related Background Art
Conventionally, in an electrophotographic image forming apparatus using the electrophotographic image forming process, there has been adopted a process cartridge system in which an electrophotographic photosensitive member as an image bearing member and a process means acting on the electrophotographic photosensitive member are integrated into a cartridge, which is detachably mountable to the electrophotographic image forming apparatus main body. In the process cartridge system, the maintenance of the apparatus can be conducted by the user without relying on a serviceman, thus achieving a substantial improvement in operability. Accordingly, the process cartridge system is widely used.
As disclosed, for example, in U.S. Pat. No. 5,790,923, in a process cartridge as described above, a photosensitive drum 1 is integrated with a process means acting thereon and composed of a charging roller 2, a developing sleeve 5, and a cleaning means.
The developing sleeve 5 carries a magnetic mono-component developer (toner) to the photosensitive drum 1, to which a developing bias is applied, thereby developing an electrostatic latent image formed on the photosensitive drum 1.
That is, the developing sleeve 5 is rotatably supported in a toner container 3. Inside the developing sleeve 5, there is provided a magnet roller 6, which is a magnet for causing the developing sleeve 5 to carry developer.
The toner is caused to adhere to the surface of the developing sleeve 5 by the magnetic force of the magnet roller 6. After the toner layer thickness has been regulated to a fixed level by a developing blade 7, the toner is conveyed to a position where it is opposed to a latent image on a photosensitive drum 10, and adheres to the latent image to thereby effect development.
In this process cartridge, seal members 13 for preventing leakage of toner to the exterior of a developing region D are provided at the ends of the developing sleeve 5.
The seal members 13 are magnetic seal members arranged with predetermined gaps between themselves and the developing sleeve 5. Concentrated magnetic fields are formed between the magnetic seal members 13 and the magnet roller 6, and toner is allowed to stay in the gaps between the seal members 13 and the developing sleeve 5, forming magnetic brushes. Due to this arrangement, leakage of toner from the toner container 3 is prevented.
However, when the developing sleeve 5 rotates, the toner tends to move outwards in the longitudinal direction of the developing sleeve 5. In view of this, a scraping member 17 is arranged in order to return the toner adhering to the longitudinal end portions of the developing sleeve 5 to the central portion with respect to the longitudinal direction again. The scraping member 17 is provided on the downstream side of the seal members 13 with respect to the rotating direction of the developing sleeve 5. A forward end portion 17a of the scraping member 17 is counter directionally in contact with the developing sleeve 5 with respect to the rotating direction of the developing sleeve 5. The forward end portion 17a is tapered so as to be capable of scraping and collecting the toner toward the longitudinal center when the developing sleeve 5 rotates.